Guide mechanism for a magnetic head positioning devices

ABSTRACT

A guide mechanism of a positioning device for a magnetic head moving apparatus providing both improved guiding accuracy and reduced manufacturing cost. The mechanism includes a cylindrical bearing, a guide rod passing slidably through the bearing, a movable base, and grip pieces for holding the cylindrical bearing. Preferably, the cylindrical bearing is provided with one or more cylindrical recesses on its inner periphery to space portions of the bearing from the guide rod.

This is a division of application Ser. No. 838,731, filed Mar. 11, 1986,now U.S. Pat. No. 4,783,708.

BACKGROUND OF THE INVENTION

The present invention relates to a guide mechanism of a positioningdevice for a magnetic head moving apparatus.

In flexible ("floppy") disk storage systems in current widespread use, arecording/playback magnetic head must be accurately positioned relativeto the center of rotation of the floppy disk in order to ensurecompatibility between different floppy disks and floppy disk drives.

FIG. 1 is a top view of a magnetic head positioning apparatus with aconventional guide mechanism, and FIG. 2 is a sectional view taken on aline II--II in FIG. 1. In FIGS. 1 and 2, a magnetic head 1 for recordingand playing back data is moved in the radial direction along the surfaceof a floppy disk 2, the magnetic head 1 being held by a movable base 3forming a positioning device. The movable base 3 is constructed fromengineering plastics by precision injection molding. Two bearings 5a, 5bhaving excellent slide properties are respectively fitted into holes 4a,4b in holder devices 3a, 3b installed at opposite ends of the movablebase 3. Specifically, bearings of self-lubricating Teflon oroil-impregnated sintered bearings 5a, 5b are press-fitted into therespective holes 4a, 4b, or inserted therein with an adhesive, so thatthe bearings 5a, 5b are held on and incorporated with the movable base3.

A guide bar 6 slidably passing through the bearings 5a, 5b constitutes aguide mechanism for the movable base 3. The magnetic head 1 coupled toone face of the movable base 3 is thus moved and positioned as desiredby activating a driving motor 7 so as to cause it to rotate through agiven displacement angle. Since such a positioning method and anarrangement can be implemented simply using a conventional mechanism, adetailed description thereof will be omitted. Briefly, however, acombination of a threaded shaft 7a and a bearing 3c engaged therewithmay be employed. Supporting devices 6a, 6b are used to support the guidebar 6.

In the conventional magnetic head moving apparatus, an extremely highdegree of precision is required for the holes 4a, 4b at the two ends ofthe movable base 3, specifically, for their inner diameter dimension(roundness if they are round holes) and their concentricity (alignment).As forming the movable base 3 completely of metal is costly, engineeringplastic materials having a low deformability due to thermal shrinkageare selected to provide an inexpensive movable base 3 using precisioninjection molding.

However, it is difficult to make the holes 4a, 4b of the holder devices3a, 3b truly round using ordinary precision injection moldingtechniques, and hence it is necessary to employ a specially shaped orcomplicated and expensive die for the injection molding process, orotherwise it is necessary to employ additional machining for correctingthe dimensions of the holes 4a, 4b after an ordinary molding operationto attain the required precision of the inner diameter, roundness andconcentricity. Consequently, the movable base 3 has been an expensivepart.

SUMMARY OF THE INVENTION

The present invention is intended to solve the above-discussed problems,and it is therefore an object of the invention to provide aninexpensive, high-precision guide mechanism.

The guide mechanism according to the present invention is characterizedin that a cylindrical bearing extending in the longitudinal direction isheld by holder means installed in the longitudinal direction of amovable base and a guide bar passes through the cylindrical bearing, theholder means being grip pieces incorporated with the movable base andused to sandwich and clamp the cylindrical bearing. The cylindricalbearing sandwiched between and clamped by the grip pieces is caused toslide along the guide bar.

The guide mechanism according to a second of the present invention ischaracterized in that a cylindrical bearing extending in thelongitudinal direction is held by at least two holder means installed inthe longitudinal direction of a movable positioning device and a guidebar is passed through the cylindrical bearing, an indentation beingformed in the cylindrical bearing. The cylindrical bearing held by theholder means is caused to slide along the guide bar. The slidingproperties of the bearing are significantly imposed due to the presenceof the indentation provided in the cylindrical bearing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is top view of a magnetic head moving apparatus with aconventional guide mechanism;

FIG. 2 is a sectional view taken on a line II--II in FIG. 4;

FIG. 3 is a top view of a magnetic head moving apparatus employing aguide mechanism embodying the present invention;

FIG. 4 is a sectional view taken on a line IV--IV in FIG. 1;

FIG. 5 is an elevational view of the movable base of FIG. 1;

FIG. 6 is a top view of a magnetic head moving apparatus with a guidemechanism constructed according to a second embodiment of the presentinvention;

FIG. 7 is a perspective view of essential portions of the apparatus ofFIG. 6;

FIG. 8 is a sectional view taken on a line VIII--VIII in FIG. 6; and

FIG. 9 is a sectional view of a magnetic head moving apparatus accordingto a third embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the accompanying drawings, preferred embodiments of thepresent invention will be described. Like reference numerals andcharacters designate like or corresponding elements of theabove-described conventional apparatus, and hence a further descriptionthereof will be omitted.

FIG. 3 is a top view of a magnetic head moving apparatus including aguide mechanism embodying the present invention, FIG. 4 is a sectionalview taken on a line IV--IV in FIG. 3, and FIG. 5 is an elevational viewof the movable base.

In FIGS. 3 through 5, a movable base 8 embodying the present inventionis formed with a thin metal sheet formed into a box shape as shown inFIG. 5. The movable base 8 is provided with a magnetic head fitting hole9 in its upper face and three grip pieces 8a, 8b, 8c whose centralportions are bent in a semicircular shape as shown. The grip pieces thusformed are precisely positioned relative to the movable base 8 and arecapable of providing the cylindrical bearing 11 with highly precisemounting at a low cost.

The outer periphery of the cylindrical bearing 11 is sandwiched betweenthe grip pieces 8a, 8b, 8c as part of the side of the movable base 8,held by bonding, adhesive, or by press-fitting. The grip pieces 8a, 8b,8c are about 0.4 mm thick. An oil-impregnated sintered bearing isemployed as the cylindrical bearing 11. As the cylindrical bearing 11has an outer diameter of about 5 mm, a sheet thickness of 0.3 mm and alength of about 40 mm are suitable. In this case, the grip pieces 8a,8b, 8c exceed the cylindrical bearing 11 in bending strength,compression strength and torsion strength. The precision parts of thecylindrical bearing 11 enhance the guiding properties of the movablebase 8 and the guide bar 6. Moreover, the use of an oil-impregnatedsintered bearing as the cylindrical bearing 11 provides greaterroundness and attains a longer service life than in the conventionalcase. Consequently, the guide mechanism embodying the present inventionis capable of providing an inexpensive magnetic head moving apparatuswith precision and with a reliability higher than conventionalapparatuses employing engineering plastic materials.

As set force above, the invention is characterized by a cylindricalbearing extending in the longitudinal direction and held by a holderdevice installed in the longitudinal direction of a movable base, and aguide bar passing through the cylindrical bearing, grip pieces combinedwith a movable base being employed as the holder means for sandwichingand clamping the cylindrical bearing. Accordingly, an inexpensivehigh-precision guide mechanism is obtained according to the presentinvention.

FIG. 6 is a top view of a magnetic head moving apparatus constructionaccording to a second embodiment of the present invention, FIG. 7 is aperspective view of an essential portion of the same, and FIG. 8 is asectional view taken on a line VIII--VIII in FIG. 6.

In FIGS. 6 through 8, a movable base 8 embodying the present inventionis equipped with U-shaped holder devices 12a, 12b at opposite ends ofthe movable base 8 spaced in the direction of movement of the base 8.According to this embodiment of the present invention, there is provideda cylindrical bearing 13 adhesion bonded along outer peripheral portionsat the opposite ends thereof to the inner peripheries of the holes 14a,14b of the holder devices 12a, 12b, whereby the cylindrical bearing 13is fixed to the holder devices 12a, 12b. The cylindrical bearing 13 isan oil-impregnated sintered bearing, the ends of which have a diametercorresponding to the diameter of the guide bar 6 and the holes 14a, 14bof the holder devices 12a, 12b, to thus form faces 13a, 13b makingcontact with the guide bar 6. An indentation 13c is formed between thefaces 13a, 13b, the inner periphery of which is spaced from the guidebar 6.

Since the bearing is a metal cylindrical part, it is easy to ensure, forinstance, an inner bearing hole diameter of 4±0.004 mm, a roundness offby no more than ±0.004 mm, on a concentricity off by no more than±0.005/40. Accordingly, the movements of the guide bar 6 and thecylindrical bearing 13, namely, the guide bar 6 and the movable base 8,are precisely controlled; that is, their movements are not adverselyaffected by the rigidity and machining precision of the portions closeto the holes 14a, 14b of the movable base 12. Since the areas of thecylindrical bearing 13 in contact with the guide bar 6 are only thoselocated at the opposite ends thereof, the viscosity resistance (which isgenerally proportional to the contact area of the oil-impregnatedsintered bearing) is reduced. Moreover, since the holes 14a, 14b can besomewhat U-shaped, the die for casting the movable base 12 can be simplyformed of upper and lower dies. Accordingly, a reduction in the cost ofthe dies is achieved and their service life improved. Thus, thisembodiment of the invention provides an inexpensive precision magnetichead moving apparatus.

FIG. 9 is a sectional view of a third embodiment of the presentinvention, wherein there is formed a mid-position contact area 13d inaddition to those 13a, 13b at the opposed ends of the cylindricalbearing 13 in contact with the guide bar 6. The same effects as in thepreceding embodiment are attained, although with a viscosity resistancesomewhat greater than in the preceding embodiment.

The second and third embodiments of the invention are thus characterizedby a cylindrical bearing extending in the longitudinal direction andheld by at least two holder devices installed in the longitudinaldirection of a movable positioning device, and a guide bar passingthrough the cylindrical bearing, an indentation being formed in thecylindrical bearing. An inexpensive high-precision guide mechanism isthus obtained according to the present invention without impairing thesliding properties of the bearing and the guide bar.

I claim:
 1. A guide mechanism of a positioning device for a magnetichead moving apparatus, comprising: a cylindrical bearing; a guide rodpassing slidably through said bearing, said bearing having at least onecylindrical indentation formed in an inner periphery of a centralportion thereof; a movable base; and means for holding said cylindricalbearing to said movable base.
 2. The guide mechanism of claim 1, whereinthere are provided two of said indentations.
 3. The guide mechanism ofclaim 1, wherein said bearing comprises an oil-impregnated sinteredbearing.